The present invention relates to an over voltage protection circuit for interconnection between electric equipment and a source of electrical power, typically alternating current.
Transient voltage surge suppressors (TVSS) are often included between the electric power lines and electrical equipment connected to such power line. The purpose of these surge suppressors is to protect the electrical equipment from surges and other transients due to lightning, switching impulses and other complications from the power lines. These suppressors protect by blocking the surges before they reach the electrical equipment connected to the power line. The protectors themselves normally protect for a 6,000 volt, 500 amp, 20 micro-second pulses. These pulses are the largest that were once expected to occur on an interior outlet in a 120 volt AC 15 amp distribution circuit. Surge suppressors built to this withstand level were thought to have protection against lightning strikes and other known transients and surges. A common surge protection method is to include a voltage limiting device between line and neutral. In most protectors, this meant utilizing a metal oxide varistor (MOV) in series with a thermal catastrophic fuse between line and neutral. In this device, if the incoming over voltage is strong enough to damage the voltage limiting device, the fuse opens thereby disconnecting the voltage limiting device from the circuit and preventing its destruction. However, with the disconnection of the voltage limiting device subsequent transients and surges can pass directly to the electrical equipment connected to the device. Recognizing this type of operation, in well designed newer surge protectors the electrical equipment is disconnected from the line in the event of an incident of transients or surges sufficient to cause the protection circuit to overload. Such a device is shown in FIG. 7 herein. This action is said to simultaneously protect the voltage limiting device as well as the electrical equipment interconnected to the power connection. The device, however, may still suffer from leakage. Another characteristic of more recent protection designs is that the housing can remain intact after two 3,000 amp or twenty 500 amp surges, even if the protection devices or fuses have been damaged.
The present invention is to provide additional functions over and above that provided by even the new protectors in a compact, simple structure.
It is an object of this invention to disconnect the line in an overvoltage situation;
It is another object of this invention to provide for a competent multi-state power protection circuit;
It is yet another object of the present invention to increase the levels of protection of a power protection circuit;
It is still another object of the present invention to provide a mode of protection against open neutral conditions in building wiring;
It is a further object of the present invention to protect against high voltage power cross events;
It is yet another object of this invention to provide for the same measure of protection in a line to neutral reversed wiring condition;
It is another object of the present invention to provide for a dual mode power protection circuit;
It is a further object of this invention to provide for a power protection circuit which disengages power from the protected device;
It is yet another object of this invention to reduce ancillary leakage through a damaged surge protector;
Other objects of the invention and a more complete understanding of the invention may be had by referring to the drawings in which: